Among cutting tools widely used for cutting of metals, printed circuit boards, and the like, a cutting tool has been known which includes a substrate composed of a cemented carbide, a cermet, a ceramic, or the like and a single or a multiple coating layer provided on a surface of the substrate. As this coating layer, a chemical vapor deposition (CVD) film including a TiC (titanium carbide) layer, a TiN (nitride titanium) layer, a TiCN (titanium carbonitride) layer, an Al2O3 (aluminum oxide) layer, and the like laminated to each other has been used in many cases.
For example, Patent Literature 1 has disclosed a cutting insert in which a surface of a cemented carbide substrate is coated with a TiCN layer, an Al2O3 layer, and a TiC layer which are laminated in this order.
In addition, Patent Literature 2 has disclosed the structure in which a surface of a silicon nitride substrate is coated with a hard coating layer, and a first layer of the hard coating layer is a titanium nitride layer of a columnar crystal which contains a granular crystal having a crystalline grain diameter of 1 to 30 nm.
The following is a list of the aforementioned background art    PTL 1: Japanese Unexamined Patent Application Publication No. 2003-213455    PTL 2: Japanese Unexamined Patent Application Publication No. 10-015707
However, even by the structure of the coating layer disclosed in Japanese Unexamined Patent Application Publication No. 2003213455 which is composed by repeatedly laminating a TiCN (TiN) layer and an Al2O3 layer, or even by the structure as disclosed in Japanese Unexamined Patent Application Publication No. 10-015707 in which the crystalline form of a TiN layer provided right over a substrate composed of a silicon nitride-based sintered body includes both a granular crystal and a columnar crystal at a portion adjacent to the substrate, the adhesion of the coating layer was not sufficient in some cases, and in addition, chipping thereof occurred in some cases due to cracks generated in an Al2O3 layer in cutting.
The present invention was made to overcome the problems described above, and an object of the present invention is to provide a cutting tool including a coating layer which has a high adhesion and high chipping-resistant characteristics.